Final answer:
A mixing or tempering valve is used in water systems to blend hot and cold water to a safe and comfortable temperature, thereby preventing scalding.
Step-by-step explanation:
A mixing valve or tempering valve is a valve used in water systems to regulate the temperature of the hot water that comes out of fixtures like showers and sinks. It works by blending hot water with cold water to ensure that the water temperature is safe and comfortable for use. This is especially important to prevent scalding in households where children, elderly, or people with disabilities may be at risk. The correct answer to the question is C: A valve used to regulate temperature in water systems.